Yes, I've used it periodically over the last 30 years. I don't fool with Reflectix, but it is slightly tougher. There are two forms of Bubble-Pak. One has large bubbles, maybe 3/4" in diameter. The other has small bubbles, maybe 1/4" in diameter. I found the small form to work better. It seems like the small bubbles pop less.
Obviously this stuff is not tough like closed cell foam. However, it is better than nothing. I would use it only when I thought I was going to be out in mild weather conditions, because the insulating value is going to be almost zero.
On one recent trip, I had one piece of closed cell foam that was about 16" square. Then I had the small bubble type that was 18" wide by 36" long. To carry it, I roll it up and stick it under the pack lid. It's not elegant, but it works.